how to make an easel back? (i know the answer will be simple)

Ok i’m racking my head on how to do this simply, but how do you do an easel back for a photo frame? its the little flap that makes the photo sit upright. I want my easel back to be adjust able to a person can use the frame for horizontal and vertical images (so they aren’t stuck in one direction or the other)

I’m entering in a show that most of the item has to be handmade and so it’d like to make it out of wood. it seems like i should just be able to cut the flap shape and then attach a hinge from the hardware store. does that seem right?